[ENH] add autopopulation of select in customsearch for tracker field dropdown
Description
currently it's possible to autopopulate the {select} in customsearch from a tracker field as text, userSelector or itemList. this PR adds the possibility to autopopulate a tracker field dropdown too.
Steps to test
create a tracker with a dropdown field, enter dropdown options. create a customsearch with a {select} field that links to that tracker field. magic!
Expected result
if you don't specify _options/_labels in the {select}, then they will be taken directly from the tracker field options.